Tend, attend, mind, watch are comparable when they mean to take charge of or look after someone or something especially as a duty or in return for remuneration.
Tend usually retains some notion of an earlier sense in which it means to pay attention; hence, it is appropriately used in situations to which this notion is relevant.
Often it is used in reference to menial, unskilled, or routine employments and then typically takes for its object something that requires attention (as in anticipating wishes or needs, looking out for accidents, mishaps, or signs of danger, or maintaining effective mechanical operation); thus, one who tends a lock is employed to work the devices adjusting the level of the water in the canal when a boat approaches; a shepherd is one who tends a flock of sheep; a stoker tends a furnace and supplies it with fuel when needed.
Tend is used in reference to the care of persons when a menial or a ministering rather than a professional relationship is implied.
Attend , which is more likely to be colored by a sense meaning to take charge, is appropriate when the services given are of a professional character or are the prerogatives of a post that one holds as a mark of honor or merit.
Mind is closer to tend than to attend , but it distinctively suggests a guarding or protecting (as from harm, injury, or failure).
Watch (see also SEE 2 ) may come close to mind , but it tends to imply a more constant or more professional relationship and to suggest a more definite need of vigilance and usually the intention of forestalling danger.